One of the major improvements in tires in the previous century was the development of an inner liner. The presence of the inner liner, extending from bead to bead, radially inward of the tire casing, permitted the elimination of an inner tube. The inner liner is formed of a low permeability material to retain air inside the tire when the tire is properly mounted on a wheel.
Rubbers, such as butyl, bromobutyl, and halobutyl rubber, which are relatively impermeable to air are often used as a major proportion of inner liners. For instance, U.S. Pat. No. 2,676,636 discloses the use of butyl rubber as a highly air-impermeable inner liner for tires. Halobutyl rubbers are frequently employed as inner liners because they offer both excellent gas barrier properties and low temperature flexural properties.
The inner liner is normally prepared by conventional calendering or milling techniques to form a strip of uncured compounded rubber of appropriate width which is sometimes referred to as a gum strip. Typically, the gum strip is the first element of the tire applied to a tire building drum, over and around which the remainder of the tire is built. When the tire is cured, the inner liner becomes an integral, co-cured, part of the tire. Tire inner liners and their methods of preparation are well known to those having skill in such art.
Also known in the tire industry are self-supporting tires, capable of permitting travel even when the tire is underinflated. Such tires are disclosed in U.S. Pat. Nos. 4,365,659, 5,158,627, 5,368,082 and 6,453,961. A common characteristic of a self-supporting tire is the presence of rubber elements in the sidewalls of the tire. The rubber elements prevent collapse of the tire sidewall during underinflation operation.